fast, quick, active, busy,
Slow and leisurely would be synonyms.
synonym
slow, sluggish
Synonyms.
Slow and fast are antonyms; a synonym is a word with a similar meaning.
delay, wait, slow, procrastinate
Antonyms are just words like any other word you use them when it is appropriate.It is just that an antonym is a word that has an opposite for example fast and slow. We can say fast is an antonym of slow or we can say fast is the opposite of slow.
1 slow to heal.2 habitually lazy
speedy, fast, quick, nimble
dumb,slow,no sense, no mind,can't think.
Antonyms of the word "pace" include terms like "halt," "stop," and "standstill," which indicate a lack of movement or speed. Other possible antonyms are "slow" and "deceleration," representing a reduction in pace or speed.
The word "antonym" means a word that is the opposite of another. The only two words you listed that are opposites are b, fast and slow.